The hyphen helps avoid confusion by telling readers when combinations of two or more words should be understood as a single concept. These combinations, called 'compound words', have five main uses:

  1. Compound nouns:
    Hyphens can join two or more words to form new 'nouns'. These forms are typical of journalistic and business writing, though less common in academic writing.

  2. Compound adjectives:
    Hyphens can indicate that two or more words act as an 'adjective' before a noun. These forms typically occur in the academic writing of science and technology.

  3. Words formed from affixes:
    Hyphens can be used to join an 'affix' to a word. Americans tend to use this only to avoid misunderstanding, whereas the British use hyphens to separate clearly prefixes from the main part of the word.

  4. Numbers and fractions:
    Hyphens are used to form fractions (one-third) and compound numbers (from twenty-one to ninety-nine).

  5. Avoiding ambiguity:
    Hyphens are used to make a clear distinction between words that would otherwise be confused re-form (to form again) and reform (to improve by change).